US Patent and Trademark Office - The US Patent and Trademark Office (PTO) is the agency within the Department of Commerce charged with implementing the US patent and trademark system. Their Frequently Asked Questions or FAQ page is available here. The US Patent and Trademark Office (USPTO) has a network of Patent and Trademark Resource Centers(PTRCs) with the resources to assist inventors with conducting both a preliminary patent or novelty search and a Federal trademark search(visit it here). An Oklahoma PTRC is at OSU in Stillwater. Full-text utility, design, and plant patents with images are available back to 1790! A recent resource available from PTO is a link including all editions and all revisions (1948-) of the Manual of Patent Examining Procedure.
European Patent Office - The European Patent Office is a centralized patent grant agency established by the Convention on the Grant of European Patents (EPC) signed in Munich 1973. A list of the participating nations can be found here.
British Library's Patent Information. One of the world's best resources for obtaining copies of patents and other forms of intellectual property.
Eurasian Patent Organization - The Eurasian Patent Organization is composed of members of the former Soviet Union.
International Federation of Inventors Association
ip.com - This is a commercial site dedicated to aspiring inventors.